During processing of microelectronic substrates, such as semiconductor wafers, selective stripping or etching away of a layer or portions of a layer or layers of the wafers may be required. A conventional technique, referred to as "wet etching" includes immersing a plurality of wafers into an etching solution and moving the wafers in various directions to enhance the etching process.
Accurate removal of material may depend on the processing time, the temperature of the etching solution and the composition of the etching solution. The temperature of the etching solution may be maintained at room temperature. The temperature of the etching solution may also be increased to improve the etching rate and to increase etching efficiency. Etching rate and efficiency may also be influenced by the cleanliness of the etching solution. In order to maintain clean etching solution, the etching solution may be recirculated and filtered using a pump and a filter.
FIG. 1 illustrates an embodiment of a conventional wet etching apparatus for processing semiconductor wafers. The wet etching apparatus includes: an inner container 11 configured to receive semiconductor wafers 25; an outer container 12 connected to the upper peripheral portion of the inner container 11; and a recirculation line 13 in fluid communication with both the inner and outer containers. The etching solution is recirculated in the direction indicated by the arrow 19. Specifically, etching solution overflows from the inner container 11 to the outer container 12, down through the recirculation line 13 and filter 15, and is pumped back into the inner container via a pump 14. Discharge lines 17 may be connected to respective discharge valves 16, as illustrated, so that used etching solution, particles and other contamination generated during the etching processing can be discarded from the recirculation line 13. Accordingly, the inner container 11 may be provided with etching solution free of contaminants, particles and the like.
Unfortunately, various by-products of the etching process, such as photoresist particles, may subside on the bottom of the inner container 11. During recirculation of the etching solution, these particles may be forced up through the wafers, potentially contaminating the wafers. Because contamination may decrease production yields of the semiconductor wafers, there is a demand for a wet etching apparatus that can reduce recontamination of the wafers inside the wet etching apparatus during the etching process.